1. Field of the Invention
This invention relates to electrical discharge machining apparatus and more particularly to such apparatus having electrode management systems to compensate for electrode wear.
Various servo-controlled hydraulic and electric drive motors have been proposed for use in electrical discharge machining apparatus to position an electrode feed system in an anti-short position to produce a predetermined gap between the electrode and workpiece at initiation of an EDM feed cycle.
2. Description of the Prior Art
One such system is shown in U.S. Pat. No. 3,601,572 issued Aug. 24, 1971 for Electrode-Replenishing Apparatus for Electrical Discharge Machine. In such apparatus, a wire electrode spool is supported on a movable carriage which also carries a pair of electrode feed rollers which feed the wire from the spool during electrode replenishment.
The apparatus in U.S. Pat. No. 3,601,572 requires a separate hydraulic cylinder to produce a first "anti-short" movement of the roller carriage. Refeed of the electrode follows. When the electrode reaches the workpiece, movement of the roller carriage is reversed in an amount equivalent to the prior anti-short forward motion.
U.S. Pat. No. 3,531,616 discloses a servo control circuit for maintaining a constant gap between the tip of a fixed electrode and a workpiece which is subjected to electrical discharge machining.
U.S. Pat. No. 2,818,491 discloses a control means for compensating for wear of electrodes for grinding a workpiece; said control means having means for sensing gap changes and servo means that are driven in response to gap changes to compensate for electrode wear.
U.S. Pat. No. 4,361,745 discloses use of a microprocessor to control the machine operation of an electrical discharge machining apparatus.
U.S. Pat. No. 3,125,700 discloses a servo mechanism to adjust for electrode wear in an EDM machine by adjusting the position of an electrode holder in increments to maintain the servo mechanism in an optimum range for EDM operation.
Such prior art systems either do not provide for electrode erosion compensation or if compensation is provided, require use of at least two servo drives; one to move the electrode during a machining operation and the other to adjust the position of the electrode to compensate for its erosion during the machining operation.